In recent years, manufacturing technologies for display devices have matured and manufacturing costs have decreased. As a result, display devices of various sizes are available worldwide. Current design efforts are now focused on enhancing image quality of display devices and providing display characteristics that better meet user requirements.
Generally, a maximum image resolution (i.e., the number of pixels of an image in a vertical direction and in a horizontal direction) displayed by a display device is constant. However, original resolutions of video signals provided by various signal sources, e.g., a DVD player, a cable of a cable TV, or a wireless TV antenna, connected to the display device are different. In order to match with a resolution specification of the display device, the signal source apparatus for providing video signals may adjust in advance a size (i.e., a resolution) of an output image to match with a size of a screen of the display device.
It is known to a person having ordinary skill in art that the number of pixels of a low-resolution image needs to be increased so as to convert the low-resolution image to a high-resolution image. For example, in order to convert an image from a resolution of 800*600 pixels to a resolution of 1200*900 pixels, an image processing apparatus needs to interpolate 400 pixels into each row of the image, and interpolate 300 pixels into each column of the image. Gray-scale values of the interpolated pixels are mostly determined according to an interpolation calculation.
Gray-scale variations obtained by enlarging the size of the image via the interpolation calculation are quite gradual, in a way that such image may appear blurred to an observer. When a difference between the original resolution and the converted resolution is too large, the image quality may easily seem apparently unsatisfactory to the observer. However, since current display devices cannot determine whether the image is processed by a resolution conversion process according to its received signals, the foregoing problem of unsatisfactory image quality cannot be avoided.